The term "electroerosion" is used herein to refer to a machining process in which electric energy is supplied across a machining gap formed between a tool electrode and a conductive workpiece and flushed with a machining fluid to remove material from the workpiece by the action of successive time-spaced electrical discharges effected across the gap (electrical discharge machining or EDM), the action of electrochemical or electrolytic solubilization (electrochemical machining or ECM) or a combination of these actions (electrochemical-discharge machining or ECDM). In EDM, the machining fluid is commonly a liquid which is basically electrically nonconductive or of dielectric nature and typically constituted by deionized water, a liquid hydrocarbon or a combination of such water and hydrocarbon. The electric energy is supplied commonly in the form of a succession of voltage pulses which result in a corresponding succession of pulsed, discrete electrical discharges across the machining gap. In ECM, the machining fluid is commonly a liquid electrolyte which is naturally conductive, and the machining current may be a direct current but is preferably in the form of pulses or pulsating current. In ECDM, the machining fluid is typically a liquid having both dielectric and electrolytic natures and may be tap water or water deionized to retain weak conductivity.
In traveling-wire (TW) electroerosion, the tool electrode is constituted by a continuous electrode element which is typically a conductive wire having a diameter ranging from 0.05 mm to 0.5 mm, but may take the form of a tape or ribbon of similar thickness. Such electrode is broadly and generally referred to herein also as a wire-like electrode. In the TW electroerosion process, the continuous electrode is continuously dispensed from an electrode supply, e.g. a wire reel, to continuously travel along a straight-line path traversing and defined across the workpiece and is eventually collected into or onto collection means, e.g. a takeup reel. This straight-line path is established by at least one pair of guide members disposed across the workpiece to maintain the traveling electrode as straight as possible and precisely in erosive cutting relationship with the workpiece across the machining gap flushed with the machining fluid while the straight-line path and the workpiece are relatively displaced along a programmed cutting path as electroerosion proceeds across the gap. It is thus critical to ensure that these guide members are properly arranged and positioned relative to a prescribed instantaneous position of the workpiece inasmuch as these positioning members directly affect the accuracy of cut which is to proceed with the programmed cutting path.
The machining liquid is continuously supplied into the machining gap typically by means of a pair of nozzle assemblies which are disposed at the opposite sides of the workpiece. It is desirable that each assembly have a nozzle outlet open towards the machining gap and the nozzle outlet accommodate the traveling electrode therein so that the machining fluid is discharged, as an envelop flow surrounding the electrode, towards the workpiece and into the machining gap. This arrangement has been found to be advantageous to serve to maintain the required linearity of the traveling wire, promote renewal of the machining fluid and to cool the electrode and the workpiece, in the cutting zone. The electrode and the workpiece tend to be heated up by the electrical discharge or high-density machining current. The electrically energized length of the electrode tends also to be heated up because of the small cross-sectional area of that length through which such current must pass.
The electroerosive energization of the machining gap is thus established by connecting one terminal of an erosion power supply electrically with the electrode and its other terminal electrically with the workpiece. The electrode and the workpiece can be energized by bringing the electrical contacts for the electrode and the workpiece into respective contact with the two terminals of the electric power supply. During the machining operation it is critical that these members be held in proper electrical contact with the traveling electrode and the workpiece and that the energized portions of the latter two be held in proper cooling contact with the machining fluid. This also requires consideration as to how the guide members should best be arranged and their positions maintained. Also, in initiating the gap energization it is critical to ensure that these members are properly positioned and the nozzle means commence operating to properly flush the gap with the machining fluid before the gap is electrically energized. While various systems have so far been proposed or suggested as to these essential elements in TW electroerosion machines, it has been found that they both individually and in combinations fail to meet the foregoing critical requirements to achieve an optimum TW-electroerosion result.